Method of exhausting thermionic tubes and like devices



I I Patented Nov. 29 1927.

umen STA on the walls of of speeding up the'last step 0 eration and second y t TES PATENT OFFICE.

OI OAKLAND,

CALIFORNIA, ASSIGNOR TO THE MAGNAVOX CALIFORNIA, A CORPORATION OF ARIZONA.

METHOD OI EXHAUSTING THEBMIONIO TUBES AND LIKE DEVICES.

No-Drawing.

and more particularly as from the filament.

The usual method of eliminating gas from the filament device is a small over-voltage process usually This invention relates to a method of ex hausting thermionic tubesand other devices to the elimination of to burn the filament at during the exhausting at the last moment, as the gas eliminated at that period may thereby be pumped out. l

Great difficulty is ing out or removing thus evolved. The

experienced in pumpsmall amounts of gas final exhausting of a thermionic device often includes the vaporization of calclum or magnesium to absorb or clean up residual gases.

are commonlyreferre 'may be, vaporized by two lst-by heating the getter I heating device or second etter as an anode and lighting eddy current using the g the filament, thus heatin In the first method may be lit If before, y getter is left on very detrimental to most to the oxide coated type or any such larly These materials d to as a etter and usua methods by means of an y by bombardment.

emp oyed, the filament either before or. after vaporization. the residual gas may be removed the getter but a coating of the filament which is filaments, particuthe filaments which depend on oxides for emission. If the filament is burned after the getter not well absorbed.

method where the filament is used as a cath-- ode to vaporize the ment, it sufiers greatly residual gas and gas ment I have found that residual ment is promptly and quick that gas-is released from the vaporization and deposition of the tube, and in that manner metallic or otherwise none of the is left on the. present invention is,

is vaporized,

tter filament. The object of the as eliminated from the gas thrown outis In the second-named etter by bombardrom the action of the evolved from the filamerely adds to this detrimental action.

as in the filaabsorbed if ament during the getter accordin ly,.first that the exhaust- 0 make sure the filament is method briefly stated, congetter on the plates the plates with an eddy ther means until the :to evaporate, immedithe exhausting pump.

mined vacuum or degree of exhaustion is ob-' I Application filed Januai-yfll, 1927. Serial No. 165,045.

ately lighting the filament to a high brilllancy and cutting off the current to the eddy current device the moment the. filament 1s lighted, as the radiant heat of the filament is then sufiicient to continue the evaporation of the getter. The filament is permitted to remain lit until the getter is entirely spread and the gases emitted completely absorbed.

In actual practice, after the filament, the grate and plates have been assembled, a small amount of getter is deposited on the plates. The assembly is then enclosed in the tube in the usual manner and connected with When a predetertained the eddy current device is applied .and the plate is heated to a substantially red heat when vaporization of the getter commences. The plate heating device and the filament lighting device are preferably operated from a single handle uick throw switch so that the moment the p ate reaches vaporization temperature, the current may be switched from the eddy current device to the filament without appreciable loss of time. The radiant heat of the filament is then suflicient to continue and complete vaporization. Gas is eliminated from the filament during the actual vaporization and deposition of the getter and the gas is immediately absorbed by the getter no bombardment of any kind takes place in the tube and deposition of the getter on the filament is avoided. It is of considerable importance that the filament should not be lit during the time period that the eddy current heating device is employed.

Such gas evolved from the filament ionizes due to the voltageemployed on the eddy current coils and as such would defeat the purpose. to -wit: that of thoroughly eliminating gas from the filament without any ionization bombardment whatsoever.

The operation of finally removing the gases eliminated by the filament and theroughly absorbing the same is thus quickly and efiiciently may finally be sealed in the usual manner.

Having .thus described my invention, what I claim and desire'to secure by Letters Patent is 1. A method of absorbing gas from the filament, of a thermionic device which consists in heating a getter material within the thermionic device to a sufiicient temperaaccomplished and the tube ture to start vaporization, discontinuing said operation and immediately burning the filament so as to continue evaporation of the getter bymeans of radiant heat of the filament.

2. In a thermionic device including a plate and a filament, a method of absorbing gas eliminated by the filament, which consists in placing a small amount of getter on the plate, heating the plate to start vaporization, discontinuing said heating, the moment .sutficient temperature is obtained to start vaporization, discontinuing heating by the eddy current device the moment vaporization commences and then completing vaporization by immediately burning the filament at an over-voltage, so that vaporization may be completed by radiant heat from the. filament.

4. In a thermionic device having a filament and a cooperating electrode, a method ,of absorbing gas eliminated by the filament which consists in placing a piece of magnesium or other evaporating getter material on the electrode, heating the electrode to start vaporization, discontinuing the heater the moment vaporization commences, then immediately lighting the filament so that the radiant heat will continue vaporization and continuing the burning of the filament until vaporization stops.

HERBERT E. METCALF. 

